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[en] With their current conventional weapons, it is impossible for the Chinese to check a Soviet invasion. And, given China's defense technology and the priority of economic development, the prospect of a rapid defense modernization is also not too good. More importantly, since China has changed from a revolutionary power into a status quo power, it can no longer lure the enemy deep and use the strategy of people's war to sink the enemy. Under these circumstances, China has no choice but to use nuclear weapons for national defense. Resting national security on nuclear weapons is a matter of necessity rather than of choice to China. But his strategy unavoidably conflicts with another of China's needs: the need to polish its peace-loving image. To extricate itself from the dilemma, China has chosen to actively participate in the game of arms control - a tactic that can make China appear peace-loving and, if it really leads the superpowers to cut their nuclear arsenals, can also bolster China's national security. In fact, even if Chinese participation in arms control does not force the superpowers to cut their nuclear weapons, it has already encouraged the mounting global anti-nuclear movement, and increased the pressure on the superpowers
[en] Purpose: The dose in the buildup region of a photon beam is usually determined by the transport of the primary secondary electrons and the contaminating electrons from accelerator head. This can be quantified by the electron disequilibrium factor, E, defined as the ratio between total dose and equilibrium dose (proportional to total kerma), E = 1 in regions beyond buildup region. Ecan be different among accelerators of different models and/or manufactures of the same machine. This study compares E in photon beams from different machine models/ Methods: Photon beam data such as fractional depth dose curve (FDD) and phantom scatter factors as a function of field size and phantom depth were measured for different Linac machines. E was extrapolated from these fractional depth dose data while taking into account inverse-square law. The ranges of secondary electron were chosen as 3 and 6 cm for 6 and 15 MV photon beams, respectively. The field sizes range from 2x2 to 40x40 cm2. Results: The comparison indicates the standard deviations of electron contamination among different machines are about 2.4 - 3.3% at 5 mm depth for 6 MV and 1.2 - 3.9% at 1 cm depth for 15 MV for the same field size. The corresponding maximum deviations are 3.0 - 4.6% and 2 - 4% for 6 and 15 MV, respectively. Both standard and maximum deviations are independent of field sizes in the buildup region for 6 MV photons, and slightly decreasing with increasing field size at depths up to 1 cm for 15 MV photons. Conclusion: The deviations of electron disequilibrium factor for all studied Linacs are less than 3% beyond the depth of 0.5 cm for the photon beams for the full range of field sizes (2-40 cm) so long as they are from the same manufacturer
[en] Radiation dose monitoring solutions have opened up new opportunities for medical physicists to be more involved in modern clinical radiology practices. In particular, with the help of comprehensive radiation dose data, data-driven protocol management and informed case follow up are now feasible. Significant challenges remain however and the problems faced by medical physicists are highly heterogeneous. Imaging systems from multiple vendors and a wide range of vintages co-exist in the same department and employ data communication protocols that are not fully standardized or implemented making harmonization complex. Many different solutions for radiation dose monitoring have been implemented by imaging facilities over the past few years. Such systems are based on commercial software, home-grown IT solutions, manual PACS data dumping, etc., and diverse pathways can be used to bring the data to impact clinical practice. The speakers will share their experiences with creating or tailoring radiation dose monitoring/management systems and procedures over the past few years, which vary significantly in design and scope. Topics to cover: (1) fluoroscopic dose monitoring and high radiation event handling from a large academic hospital; (2) dose monitoring and protocol optimization in pediatric radiology; and (3) development of a home-grown IT solution and dose data analysis framework. Learning Objectives: Describe the scope and range of radiation dose monitoring and protocol management in a modern radiology practice Review examples of data available from a variety of systems and how it managed and conveyed. Reflect on the role of the physicist in radiation dose awareness.
[en] An atomic structure software package has been implemented for the prediction of atomic properties, with special emphasis on the calculation of data related to bound state transitions, both allowed and forbidden. The present software package is based on the MCHF method for including correlation effects and the Breit-Pauli approximation for relativistic corrections, a method we refer to as MCHF + BP. A database system is described for MCHF=BP results. The wavelengths reported will not be of ''spectroscopic accuracy'' and the f-values will be in error by more than 1% and possibly even 10% or more, depending on the case. But high accuracy is often not needed. In generating Grotrian diagrams graphically, for example, high accuracy is not needed. In identification of lines, by the matching of wavelengths along with lifetime information as well as closed loop analysis it was possible to make assignments, even though the theoretical wavelengths were not ''exact''
[en] The full-potential augmented plane wave plus local orbitals method within density-functional theory is used to predict that MnBi in the zincblende phase is a true half-metallic ferromagnet with a magnetic moment of 4.000μB per formula. This phase of MnBi is found to be robust against volume changes from -12% to +30% and remains qualitatively the same under various exchange-correlation approximations
[en] The preliminary investigations are reported on the characteristics of a new, high-sensitivity thermoluminescence phosphor material (LiF:Mg,Cu,Na,Si) prepared in this laboratory. The main dosimetric peak of this phosphor occurs at 197 deg. C at a heating rate of 1 deg. C s-1. The glow curve shape shows minimal differences and sensitivity remains stable when annealed in the range from 250 to 280 deg. C for 10 min. Its TL sensitivity to gamma radiation is about 30 times higher than that of TLD-100 with a residual signal 0.2% following a 260 deg. C readout at a heating rate of 15 deg. C s-1. This negligible residual signal renders LiF;Mg,Cu,Na,Si usable in unannealed form. Its TL response at both 260 deg. C and 280 deg. C are reproducible within a coefficient of variation of 2% over ten re-use cycles without systematic decrease. It retains the main advantages of LiF:Mg,Cu,P phosphor, and has a lower residual signal and a better stability to heat treatment. (author)
[en] Polyvinylpyrrolidone (PVP- )capped rutile GeO2 nanoparticles were synthesized through a facile hydrothermal process. The obtained nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), thermo gravimetric analysis (TGA), and photoluminescence spectroscopy (PL). The capped GeO2 nanoparticles showed significantly enhanced luminescence properties compared with those of the uncapped ones. We attributed this result to the effect of reducing surface defects and enhancing the possibility of electron-hole recombination of the GeO2 nanoparticles by the PVP molecules. PVP-capped GeO2 nanoparticles have potential application in optical and electronic fields.
[en] Glass forming ability/range of the Mo-Pd binary metal system was studied by thermodynamic calculations employing Miedema's model and ion beam mixing of multiple metal layers. The thermodynamic calculations predict a narrow composition range of 8-26 at% Pd, within which metallic glass formation is energetically favored, whereas the experimental results showed that ion beam mixing was able to synthesize metallic glasses within a composition range 13-30 at% Pd, which was well in accordance with the prediction. Besides, in the Mo70Pd30 multilayered films, with varying the irradiation dose, a dual-phase metallic glass was formed, and it could be considered as an intermediate state. The possible mechanism for the formation of the metallic glasses was also discussed in terms of the atomic collision theory.